Research Article |
Corresponding author: Ivana Karanovic ( ivana@hanyang.ac.kr ) Academic editor: Saskia Brix
© 2020 Hyunsu Yoo, Van Anh Le Thi, Ivana Karanovic.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Yoo H, Thi VAL, Karanovic I (2020) Two Paradoxostomatidae (Ostracoda) species from South Korea with a key to genera of the family. ZooKeys 943: 21-39. https://doi.org/10.3897/zookeys.943.52938
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Cytherois gajinensis sp. nov. is described and Violacytherois sargassicola (Hiruta, 1976) is redescribed. The species have been collected from littoral and interstitial waters in South Korea. They belong to Cytheroisinae, one of the three Paradoxostomatidae subfamilies. Both species are the first taxonomic records of the subfamily in Korea. Taxonomic keys to the living Paradoxostomatidae genera are provided in an attempt to clarify the position of some of the currently included genera as well as a key to East Asian Cytheroisinae species in order to facilitate further biodiversity research in the region.
Biodiversity, Cytheroisinae, East Asia, taxonomy
The family Paradoxostomatidae comprises ostracods with a fragile, elongated, and laterally compressed carapace (
According to the World Ostracoda Database (
Although South Korean cytheroids are poorly studied in general (see
Here we report on two Cytheroisinae species from South Korea. One is a new species of Cytherois and the other is Violacytherois sargassicola (Hiruta, 1976). Cytherois is by far the most diverse genus in the subfamily comprising about 60 species (see
Both Flabellicytherois and Chelonocytherois are monospecific and endemic to East Asia (
Beside the description and redescription of two Cytheroisinae species, we also provide a key to all living genera of Paradoxostomatidae and living East Asian species of Cytheroisinae.
Samples were collected by scientific scuba diving (
Abbreviations used in text and figures:
A1 Antennula;
A2 Antenna;
GF Genital field;
H Height;
Hp Hemipenis;
L Length;
LV Left valve;
L5-7 Leg 5-7;
Md Mandibula;
Mxl Maxillula;
RV Right valve.
Superfamily Cytheroidea Baird, 1850
Family Paradoxostomatidae Brady & Norman, 1889
Genus Cytherois Müller, 1884
Holotype , male, dissected on one slide (NIBRIV0000813439) and shell on micropalaeontological slide; allotype, female, dissected on one slide and shell on micropalaeontological slide; paratypes: two males dissected on each slides and shell on micropalaeontological slides, one female dissected on one slide and shell on micropalaeontological slide and five specimens kept in a 2 ml vial.
Type locality. South Korea, Gangwon-do, Goseong-gun, Jugwang-myeon, Gajin-ri; 38°18.16'N, 128°34.36'E, 25 m, sandy bottom; 29 Aug. 2016, collected by Raehyuk Jeong and Wonchoel Lee.
Etymology. The species is named after the beach from where it was collected.
Carapace
(Figs
A1
(Fig.
A2
(Fig.
Md
(Fig.
Mxl
(Fig.
L5
(Fig.
L6
(Fig.
L7
(Fig.
Hp
(Fig.
Carapace
(Fig.
A2
(Fig.
GF
(Fig.
All other appendages same as in male.
Cytherois sargassicola Hiruta, 1976: 24, figs 1–3.
Violacytherois sargassicola (Hiruta): Schornikov, 1993: 181, figs 7, 8; pl II, figs 7–10.
Male, dissected on one slide (NIBRIV0000813440) and shell on micropalaeontological slide; Female, dissected on one slide and shell was broken; two males dissected on one slide each, shell broken; one female dissected on one slide, shell broken; one juvenile dissected on one slide; shell on micropalaeontological slide and 12 specimens kept in 2 ml vial in alcohol.
South Korea, Gyeongsangnam-do, Goseong-gun, Donghae-myeon, Dongdong beach; 34°59.63'N, 128°26.02'E, 0.5 m depth; 04 Apr. 2012; collected by Tomislav Karanovic and Ivana Karanovic.
Carapace
(Figs
A1 and A2 same as in male (see description below).
Md
(Fig.
Mxl
(Fig.
L5
(Fig.
L6
(Fig.
L7
(Fig.
GF
(Fig.
A1
(Fig.
A2
(Fig.
Hp
(Fig.
Other appendages same as in female.
1 | Md-palp transformed into whip-like seta | Paracytherois Müller, 1894 |
– | Md-palp with distinct segments | 2 |
2 | Md-coxa styliform | 3 |
– | Md-coxa with distinct teeth | 16 |
3 | Terminal claw on A2 as well as claws on all walking legs very short and hook-shaped | 4 |
– | Terminal claw on A2 as well as claws on all walking legs not so short and hook-shaped | 6 |
4 | Mxl with only one endite | Asterositus Tanaka & Arai, 2017 |
– | Mxl with two prominent endites | 5 |
5 | Terminal segment of A2 reduced (i.e. completely fused with terminal claw) | Echinophilus Schornikov, 1973 |
– | Terminal segment of A2 not reduced (i.e. there is a clear division between the segment and the claw) | Echinositus Schornikov, 1973 |
6 | Terminal segment of A2 with 2 claws | 7 |
– | Terminal segment with one claw | 10 |
7 | Hinge lophodont | Boreostoma Schornikov, 1993 |
– | Hinge adont | 8 |
8 | Carapace with a postero-ventral spinula | Calcarostoma Schornikov & Keyser, 2004 |
– | No postero-ventral spinula present | 9 |
9 | Mxl palp completely absent | Lanceostoma Schornikov & Keyser, 2004 |
– | Mxl palp reduced into a seta | Paradoxostoma Fischer, 1855 |
10 | Hinge adont | 11 |
– | Hinge lophodont | 13 |
11 | Posterior end of carapace with extension situated slightly above middle, anterior margin cuneiform | Austroparadoxostoma Hartmann, 1979 |
– | Both anterior and posterior margins rounded | 12 |
12 | Mxl palp reduced into a medium size seta | Pontostoma Schornikov & Keyser, 2004 |
– | Mxl palp absent | Brunneostoma Schornikov, 1993 |
13 | Terminal segment of A2 carrying a seta, at least half as long as the claw | Obesostoma Schornikov, 1993 |
– | If present, seta is tiny | 14 |
14 | First endite on the Mxl at least ½ as long as the other two | Bradystoma Schornikov & Keyser, 2004 |
– | First endite on the Mxl much shorter | 15 |
15 | Anterior margin of the carapace cuneiform, and antero-ventral surface flattened | Acetabulastoma Schornikov, 1970 |
– | Anterior margin of the carapace rounded and antero-ventral surface not flattened | Triangulastoma Schornikov & Keyser, 2004 |
16 | Carapace with sieve-pores present | 17 |
– | No sieve-pores present | 18 |
17 | Terminal segment of Md-palp with a strong claw | Redekea de Vos, 1953 |
– | Terminal segment of Md-palp without a claw | Chelonocytherois Tanaka & Hayashi, 2019 |
18 | A2 with two strong terminal claws | Flabellicytherois Schornikov, 1993 |
– | A2 with one terminal claw | 19 |
19 | L5 with claw-like postero-distal seta, and A2 not sexually dimorphic | Violacytherois Schornikov, 1993 |
– | L5 with seta-like postero-distal seta, A2 sexually dimorphic | Cytherois Müller, 1884 |
1 | Carapace with sieve-pores present | Chelonocytherois omutai Tanaka & Hayashi, 2019 |
– | Carapace without sieve-pores | 2 |
2 | Terminal segment of A2 with 2 claws | Flabellicytherois bingoensis (Okubo, 1990) |
– | Terminal segment of A2 with one claw and at the most 1 seta | 3 |
3 | L5 with claw-like postero-distal seta | 4 |
– | L5 with seta-like postero-distal seta | 5 |
4 | A1 5-segmented (4th and 5th segments fused) | Violacytherois sargassicola (Hiruta, 1976) |
– | A1 6-segmented | Violacytherois violacea (Schornikov, 1974) and V. flavoviolacea Schornikov, 1993 |
5 | Terminal segment of L7 beside a claw carrying one additional seta (clearly visible) | 6 |
– | Terminal segment of L7 carrying only one claw | 7 |
6 | A1 5-segmented (4th and 5th segments fused) | Cytherois megapoda Schornikov, 1993 |
– | A1 6-segmented | Cytherois gajinensis sp. nov. |
7 | Dorsal margin of the carapace highly arched | Cytheoris decorata Okubo, 1980 |
– | Carapace more elliptical in lateral view | 8 |
8 | Fourth and 5th A1 segments lacking any seta posteriorly (but carrying 2 setae each anteriorly) | Cytherois ikeyai Nakao & Tsukagoshi, 2002 |
– | Fourth and 5th A1 segments carrying one seta each posteriorly (in addition to 2 setae each anteriorly) | Cytherois zosterae Schornikov, 1975 |
With the addition of Cytherois gajinensis there have been eleven Cytherois species described from East Asia, half of which are known from the shell only. Nevertheless, the shell shape of the new species is distinctly different from the fossil/subfossil ones. In addition, one of the subfossil species, C. asamushiensis from Aomori Bay in Japan (
The second species reported here, Violacytherois sargassicola, seems to be relatively widely distributed in East Asia, since it has been reported from Hokkaido (
The following three genera currently included in the family Paradoxostomatidae (see
This study was supported by a grant from the National Institute of Biological Resources (NIBR), funded by the Ministry of Environment (MOE) of the Republic of Korea (NIBR201902204). This work was also supported by two National Research Foundation of Korea (NRF) grants 2016R1D1A1B01009806 and BK21 Plus 22A20130012352. We are grateful to Prof. Wonchoel Lee and Dr. Raehyuk Jeong for collecting the material of the new species and kindly passing it to us. The sample collection was a part of the project titled ‘Improvement of management strategies on marine disturbing and harmful organisms’ funded by the Ministry of Oceans and Fisheries, Korea.